1. Field of the Invention
The present invention is concerned with improved anti-corrosion systems or products for application to metal surfaces and including epoxy and curing agent fractions dispersed in an ester-containing dispersant. More particularly, the invention is concerned with such products and methods of use thereof, wherein the epoxy/curing agent materials are dispersed in relatively fast-drying carboxylic acid ester dispersants exhibiting low volatile organic compound (VOC) levels and which substantially prevent phase separation between the components of the products.
2. Description of the Prior Art
It is well known that oil and gas wells are subject to extensive corrosion. Downhole equipment such as sucker rods, pump rods, tubing and casing are generally made of mild steel which is adversely affected by the production fluid of the well. The often high temperatures and acidic nature of the production fluids and formation waters magnifies these corrosion problems. Additionally, oil or gas-conveying pipelines are also prone to corrosion. Of course, a variety of other metal surfaces are subject to corrosion problems, in addition to oil and gas equipment.
A variety of anti-corrosion systems have been described in the past. Many corrosion inhibitors are aqueous dispersions containing a variety of components, e.g., 2-mercaptobenzothiozole, benzotriozole, tolyltriozole, phosphates, polyphosphates, organic soluble polymers, silicates, dithiocarbamates, nitrites, oxazoles, imidazoles, imidazolines, lignands, lignosulfates, tannins, phosphoric acid esters and boric acid esters. Many of these inhibitors are very prone to freezing during cold weather, making them very difficult to handle and maintain. Moreover, the useful life of many prior anti-corrosion treatments is very short, e.g., a week or less.
U.S. Pat. Nos. 5,936,059 and 5,945,164 describe highly useful anti-corrosion systems and methods particularly suited for oil and gas recovery and conveying equipment. The systems of the invention include an epoxy component as well as an amine curing agent component, which are either mixed together at the introduction site, or are simultaneously injected into a well or pipeline. A problem has arisen, however, when extremely long pipelines or deep wells require treatment. In such cases, the admixed epoxy and curing agent components tend to prematurely cure prior to application along the full length of the well or pipeline, meaning that certain portions of the equipment are not successfully treated. See also U.S. Pat. No. 4,526,813.
U.S. Pat. No. 7,407,687 describes an application technique wherein epoxy/curing agent anti-corrosion products are sequentially applied in overcome any issues of premature curing.
The prior anti-corrosion products described in the '059, '164, and '687 patents typically contain high VOC dispersants or solvents, such as xylene, toluene, or heavy aromatic napthas (HAN), and these materials can thus present an environmental issue. Moreover, these compositions may suffer from undue phase separation prior to use thereof.
There is accordingly a need in the art for improved epoxy/curing agent anti-corrosion systems or products which make use of relatively fast-drying dispersants or solvents having low VOC characteristics and which inhibit phase separation.